We are using Quectel UC20 mobile modem on a Firefly RK3399 board, but we see on all boards a poor signal. Antenna is well connected and the modem detected, but sometimes it simply does not connect to the mobile network and if it does, the signal is really low. We are using the latest Ubuntu 16.04 image.

Is there something we can do to improve the situation? Is there any other modem model that you recommend?